Roller and method for producing a roller

ABSTRACT

A roller for use in a machine for producing and/or processing and/or finishing a fiber web, such as a paper or cardboard web. The roller has a roller core and a roller cover disposed thereon. The roller cover has at least one layer or a plurality of layers. The layer or at least one of the layers is made of a foamed metal or alloy material.

The invention is based on a roller for use in a machine for manufacturing and/or processing and/or finishing a fibrous web, such as a paper or cardboard web, according to the preamble of claim 1, and on a method for manufacturing such a roller, according to the preamble of claim 13 or 14.

Rollers are employed in paper-making machines in a plurality of positions. Depending on the operating location and/or the purpose of the respective roller, said roller displays a roller covering which shows properties which are adapted to the use. In so-called calenders and smoothing mills, which may either be disposed in-line in a paper-making machine downstream of the manufacture of the fibrous web per se, or else be used off-line, usually rollers having coverings made from a composite material are applied. In earlier days, paper disks or textile disks which were placed beside one another and pushed onto a roller core and then compressed were also used.

The requirements placed on the roller coverings in the calendering sector are very high, since calenders operate with high linear loads in conjunction with high temperatures under heavy dynamic stresses.

Corresponding calender roller coverings are known from a multiplicity of publications.

For example, a roller, in particular for smoothing paper webs, which displays a hard roller core composed for example of metal and which on its outer side is provided with an elastic covering layer, comprising an elastic matrix material, which during operation is elastically deformable in regions by a counter-roller which can be pressed thereagainst, is known from DE 19928755 A1. The material and/or the construction of the elastic covering layer is selected such that in a specific temperature range and at a specific nipping frequency, as well as at an amplitude of the surface of the elastic covering layer which is caused by the deformation, the entire dissipated energy of the covering layer is minimized.

Furthermore, a roller, in particular for smoothing paper webs, which has a hard roller core which is composed of metal, for example, and which on its outer side is provided with an elastic covering layer which is composed of an elastic matrix material and of filler materials which are embedded in the matrix material, is known from DE 19925421 A1. At least part of the filler materials are configured as metallic filler materials which at least in regions are composed of metal and wherein at least part of the metallic filler materials may be configured as a metal foam.

It is mainly disadvantageous in the case of the known roller coverings here that, on account of the dissipation at high dynamic stress, the high temperature of the heating roller and the thermal-insulation effect of the known coverings, intense heating of the latter takes place. The maximum operating temperature is limited by the limitations of the material resistance. It is thus necessary for that roller that has the soft covering to be cooled during operation. This has to be noted in particular in the case of high-performance calenders. Heating of the heating roller, and cooling of the soft roller, are associated with a high expenditure of energy.

Furthermore, rollers in other positions are also exposed to heavy mechanical and thermal stresses which may cause a multiplicity of problems, ranging from cracks to partial peeling of the roller covering to damage to other components of the paper-making or cardboard-making machine, and entailing the downtimes and repair costs associated therewith. For example, high linear loads also arise in the press section where water is squeezed out of the fibrous web between rollers. The problems here often lie in the region of the bonding between the roller core and the roller covering. Connecting the various property profiles of metallic and plastic components at the interfaces is a subject matter of extensive research and development work. The so-called base layer, which serves as an intermediary between the roller core and the roller covering, correspondingly is the weakest point of the roller.

Correspondingly, it is an object of the invention to provide a roller which is suitable for the application in highly stressed positions, such as in calenders, for example, and which avoids or at least mitigates the disadvantages of the prior art. This may be achieved in particular by way of increasing the thermal conductivity and/or by increasing the thermal resilience. It is furthermore an object of the invention to provide measures which improve the bonding between the roller core and the roller covering.

With respect to the roller, the object is achieved by the characterizing features of claim 1, and with respect to the method for manufacturing such a roller, by the characterizing features of claim 13 or 14, in each case in conjunction with the generic features.

It is provided here according to the invention that the roller covering displays one or a plurality of layers, wherein the layer or at least one of the layers is formed from a foamed metallic or alloyed material.

In paper-making machines, where high linear loads are applied, in particular in press or calender positions, the use of the foamed metallic material according to the invention may make for the thermal conductivity to be increased by a multiple in comparison with conventional roller coverings, while the elastic modulus may be kept in a desirable range by way of targeted modeling of the metal foam. Heat dissipation is thus significantly more efficient than in the case of conventional roller coverings.

If the foamed metallic or alloyed material is used instead of an elastomeric material as a base layer between the roller core and the roller covering, more effective thermal dissipation which enables temperature equalization owing to the temperature, increasing on account of the high linear loads which occur, in the upper regions of the roller covering toward the roller core, can be likewise achieved.

Moreover, metal overall is more thermally resilient than composite materials. Consequently, the roller can be operated at a higher temperature, which in turn makes for an improved glazing effect to be achievable in heated calender positions, resulting in higher gloss values and less roughness. This may have positive effects on the energy requirements of the fibrous-web machine and on savings when painting the fibrous web.

Further advantageous aspects and variants of design embodiments are derived from the dependent claims.

Advantageously, the foamed metallic or alloyed material may contain aluminum, bronze, zinc, zinc alloys, aluminum alloys, such as AlSi, or mixtures from the named materials, which are distinguished by high resistance to temperatures and excellent thermal conductivity.

Advantageously, the foamed metallic or alloyed material may be configured in a substantially closed-pore manner.

Preferably, pores which are present in the foamed metallic or alloyed material may be distributed in the material in a homogeneous or almost homogeneous manner. This ensures that substantially uniform thermal dissipation can take place in the at least one layer which displays the foamed metallic material across the entire extent thereof.

According to a particularly advantageous aspect of the invention it may be provided that the pores are distributed at a gradient in the at least one layer, wherein radially inboard a comparatively low pore volume per volume unit is present, and radially outboard an increasing pore volume per volume unit is present. On account thereof, an optimal transition from the fully metallic roller core to the at least one functional layer can be achieved.

An average diameter of the pores may range from 0.1 to 1 mm.

The material advantageously displays an elastic modulus between 2000 and 10 000 MPa, preferably about 5000 MPa.

It is advantageous for the material to display a thermal conductivity of approx. 3 to 25 W/mK.

According to a preferred embodiment of the invention, the roller can display a hermetic sealing on one fibrous-web contact side. Said hermetic sealing provides for high smoothness of the fibrous-web contact side and corresponding possibilities for improving the glazing effect and/or saving thermal energy or drive output during operation of the calender.

The hermetic sealing preferably may be a filled epoxy resin having a thickness of 2 to 10 mm, or a thermal coating having a thickness of 0.05 to 0.3 mm.

An advantageous method for manufacturing a roller for use in a machine for manufacturing and/or processing and/or finishing a fibrous web, such as a paper or cardboard web, may comprise the following method steps: attaching a metal web containing a propellant on the roller core, in order to produce at least one layer, fixing the metal web on the roller core by pressing, cold rolling, or winding and adhesive bonding, supplying external heat for heating the layer containing the propellant so as to reach the melting range and, by way thereof, foaming the material of the layer.

An alternative advantageous method for manufacturing a roller for use in a machine for manufacturing and/or processing and/or finishing a fibrous web, such as a paper or cardboard web, may comprise the following method steps: cold forming of a planar semi-finished product so as to have the desired radius of the roller core, foaming by way of a thermal effect, applying the half-shell or partial-shell segments to the roller core by means of an adhesive method, in order to produce at least one layer, and connecting the segments by means of a welding or adhesive method.

According to an advantageous aspect of the invention a further method step which provides sealing of the roller covering using a hermetic sealing and which comprises the following part-steps may be provided: grinding or re-turning the roller covering and, on account thereof, opening pores of the foamed metallic material; attaching the hermetic sealing by pouring the material which forms the hermetic sealing into the opened pores. By way of a suitable selection of hermetic sealings and the viscosity thereof, the penetration depth of the hermetic sealing may be adapted to the product requirements and the position of the roller in a simple way.

In the following the invention is explained in more detail with reference to the figures, in which:

FIG. 1 shows a highly schematic illustration of a stack of calender rollers in which a roller according to the invention may be applied, and

FIG. 2 shows a highly schematic sectional illustration of a roller covering for a roller according to the invention.

In order for the measures according to the invention to be explained, a stack of calender rollers 1 for a high-performance calender for smoothing a fibrous web F is illustrated in a highly schematic manner. The rollers which are configured according to the invention, however, may also be applied in other positions, such as in the press section of a machine for manufacturing a fibrous web, for example.

The stack of calender rollers 1 which is described in an exemplary manner is formed from a plurality of rollers 2, 3, 4, which in the exemplary embodiment are disposed on top of one another in a perpendicular stacking plane. Ten rollers 2, 3, 4 are illustrated in the exemplary embodiment; however, it is also possible for more or fewer rollers 2, 3, 4 to be used, depending on the type and the quality of the fibrous web F to be processed. In practice, the stacking plane may also be inclined, for example at an angle of approx. 40 to 50°.

During the smoothing operation, the fibrous web F runs through all smoothing nips which are in each case formed by two adjacent rollers 2, 3, 4, which are pressed against one another. Between the smoothing nips the fibrous web F is guided over guide rollers 5.

The stack of calender rollers 1 in the exemplary embodiment is delimited by two soft end rollers 2, wherein a plurality of intermediate rollers 3, 4 are disposed between the end rollers 2, of which intermediate rollers 3, 4, some may be configured as hard rollers 3 and some as soft rollers 4.

The soft rollers 2, 4 either have an elastic roller sleeve which is supported from the inside, or a roller covering from plastic on a preferably metallic core or on a core from a composite material. The construction of the soft rollers 2, 4, will be discussed in more detail hereunder.

In contrast, the hard rollers 3 display a roller sleeve from metal, alternatively from a metal-coated composite material, which is heated from the inside. Heating may take place in various ways, for example by hot oil.

While during contact of the fibrous web F with a soft roller 2, 4, the contacted side is not smoothed or only modestly smoothed, contact of the fibrous web F with the hot and smooth surface of a hard roller 3 leads to intense smoothing of the contacted side under the compressive pressure in the smoothing nip.

In order for both sides of the fibrous web F to be smoothed, a so-called reverse nip 6, which is formed from two soft rollers 4, is usually configured in the middle of the stack of calender rollers 1. The fibrous web F thus is subjected to smoothing of the one side in one half of the stack of calender rollers 1, and to smoothing of the second side in the second half.

The soft rollers 2, 4, of which an exemplary embodiment is illustrated in a highly schematic manner in a sectional view in FIG. 2, usually display a roller core 10 from a metallic material, such as steel, for example, or from a composite material which may be reinforced with fibers.

A roller covering 11 which displays at least one or else a plurality of layers 12 is disposed on the roller core 10. In the case of a single layer 12, the latter simultaneously represents the fibrous-web contact face; in the case of a plurality of layers 12, the outermost of these layers 12 is suitably configured for contacting the fibrous web F.

The demands placed on the roller covering 11 are varied and characterized by sometimes extreme conditions, as already explained above. In order to fulfill its task, the roller covering 11 has to display an elastic modulus which establishes an optimal pressure profile in the smoothing nip between two rollers 2, 3, 4, across the entire axial length of the rollers 2, 3, 4.

The conventional materials which form the present prior art for this application purpose are composite materials having incorporated fiber reinforcements or, in many cases, additionally pressed paper or textile disks which are pushed onto the roller core 10 and are compressed using end disks.

The elastic modulus of the roller covering 11 for the listed applications should be in the order of approx. 5000 MPa.

In order to mitigate the above-listed disadvantages of the prior art it is proposed according to the invention to configure the layer 12 or at least one of the layers 12 from a foamed metallic or alloyed material 13.

Metals and metal alloys display a significantly higher elastic modulus than fiber-composite materials. Said elastic modulus is at values around 70 000 MPa, which is why it is necessary for it to be lowered for the desired applicability in press or calender positions. The preferable values here are in an order of approx. 2000 MPa to approx. 10 000 MPa, in particular of approx. 5000 MPa.

The metallic or alloyed material 13 is thus subjected to a treatment which allows the elastic modulus to be lowered and thus the desired property profile to be generated. To this end, for example a propellant, which produces bubbles or pores, respectively, in the material 13, is introduced into the still formable material 13 when the roller covering 11 is attached to the roller core 10. Injecting gas or sintering the material 13 may also produce the desired porous foam structure.

For the better understanding, the following general comments pertaining to the manufacture of foamed metals or metal alloys may be initially added. The manufacture of metal or alloyed foams often takes place by means of powdered metal and a metal hydride, for example titanium dihydride. Both powders are mixed with one another and then compressed by way of hot compression or extrusion so as to form a preliminary material. The preliminary material is then heated to a temperature which is above the melting point of the metal. In the course thereof, the titanium dihydride releases gaseous hydrogen and causes the mixture to foam up.

There are still other possibilities for manufacturing metal foams. For example, gas may be injected into a molten metal which, prior thereto, has been made capable of foaming by adding solid components. In order to stabilize aluminum alloys, 10 to 20% by volume of silicon carbide or aluminum oxide is added. The addition of calcium is likewise possible. Here, an increase in viscosity and, associated therewith, stabilization of the melt are achieved by the formation of the alloy.

As a further method variant, the slip-reaction foam sintering method (SRFS method) is available, by way of which above all iron, steel, and nickel foams can be manufactured. In this method, a slip is foamed by means of hydrogen which is formed by the reaction of acid with the respective powdered metal. By way of other reaction products the foam structure is set and dried in a mold. The blank thus created is subsequently sintered in a reducing atmosphere or in a vacuum.

The foaming methods which have been described above in general terms may be applied to roller coverings 11 for use in fibrous-web machines. The roller covering 11 may be manufactured from a metallic web or a metallic-alloy web containing a propellant, for example, which is attached to the roller core 10 by pressing, cold rolling, or winding and adhesive bonding, for example. Subsequently, the layer containing the propellant is heated by an external thermal effect up to the melting range of the metal or of the alloy and, on account thereof, is foamed. By way of the suitable selection of temperature control a gradient in density and in pore volume may also be produced between the roller core 10 and the surface of the roller covering 11, such that adjacent to the roller core 10 a comparatively high density with low pore volume can be observed, and radially outboard a decreasing density with relatively large pore volume can be observed.

It is likewise possible for a corresponding layer 12 to be produced by cold forming a planar semi-finished product so as to have the desired radius, and subsequently foaming the same by way of a thermal effect, and applying the half-shell or part-shell segments to the roller core 10 by means of adhesive methods. The segments may then be interconnected by means of a welding method, in as far as this has not already taken place in the course of the application by means of adhesive bonding.

Sintering of metal-coated polymer spheres, for example foamed polystyrene, also leads to a bubbly, porous structure of the metallic or alloyed material 13 showing the desired properties.

A further conceivable variant is the use of APM materials (advanced-pore-morphology materials), in particular in epoxy resin.

After curing, a structure having largely closed pores, which is distinguished by high thermal conductivity and temperature resistance and at the same time displays an elastic modulus which is adaptable to the selected position of the roller 2, 4, is created.

On account thereof, it is possible for the cooling output for the roller 2, 4 to be reduced. In the most favorable case, cooling may be entirely dispensed with. The glazing effect of the fibrous web F is significantly improved by the higher temperature of the soft roller 2, 4.

Foamed metallic or alloyed materials 13 of this type furthermore are distinguished by high absorption of impact energy and good resistance to pressure. This leads to excellent damping properties which have a vibration-inhibiting effect, to excellent mechanical stability, and thus to a long service life.

The mentioned property profiles on account of the use of the foamed metallic or alloyed material here are achievable both for inboard layers 12, as a base layer toward the roller core 10, and also for functional layers which are in contact with the fibrous web F.

The roller 2, 4, on one fibrous-web contact side, may display a hermetic sealing 15. The latter makes for high smoothness of the fibrous-web contact side and for corresponding possibilities in saving drive energy, which is particularly relevant in the calender. The hermetic sealing 15 may be a filled epoxy resin having a thickness of 2 to 10 mm, for example.

In order to achieve improved bonding of the hermetic sealing 15 to the roller covering 11, the transition between the foamed metallic material 13 and the hermetic sealing 15 may also be configured so as to be continuous, as a gradient, or by means of a transition layer. To this end, the roller covering 11 which is composed of the foamed metallic or alloyed material 13 is machined, for example by grinding or re-turning. On account thereof, part of the pores which are close to the surface are opened, on account of which the non-cured epoxy resin penetrates into the opened pores. By way of a suitable selection of the pore diameters which are close to the surface, the type of surface treatment, and the viscosity of the liquid epoxy resin which has not yet cured, the penetration depth and thus the thickness of the hermetic sealing 15 can be adjusted so as to correspond to the product requirements. The adjustment of the viscosity here may take place by suitable temperature control or by adding additives which influence viscosity.

Alternatively, the hermetic sealing 15 may also be a thermal coating having a thickness of 0.05 to 0.3 mm. 

1-15. (canceled)
 16. A roller for use in a machine for manufacturing, processing, or finishing a fibrous web, the roller comprising: a roller core; a roller covering on said roller core, said roller covering being formed of at least one layer or a plurality of layers, and said at least one layer, or at least one of said plurality of layers, being formed of a foamed metallic or alloyed material.
 17. The roller according to claim 16, wherein said foamed metallic or alloyed material is configured substantially with closed pores.
 18. The roller according to claim 16, wherein said foamed metallic or alloyed material is selected from the group consisting of bronze, zinc, aluminum, aluminum alloys, zinc alloys, and mixtures thereof.
 19. The roller according to claim 18, wherein said foamed metallic or alloyed material is AlSi.
 20. The roller according to claim 16, wherein said foamed metallic or alloyed material is formed with pores.
 21. The roller according to claim 20, wherein said pores are distributed in said material with a homogeneous or substantially homogeneous distribution.
 22. The roller according to claim 20, wherein said pores are distributed with a gradient in said at least one layer, wherein said at least one layer has a relatively low pore volume per volume unit radially inwardly, and an increasing pore volume per volume unit in a direction radially outward.
 23. The roller according to claim 20, wherein said pores have an average diameter of between 0.1 mm and 1 mm.
 24. The roller according to claim 16, wherein said material has a modulus of elasticity between 2000 and 10,000 MPa.
 25. The roller according to claim 24, wherein said material has a modulus of elasticity of about 5000 MPa.
 26. The roller according to claim 16, wherein said material has a thermal conductivity of approximately 3 to 25 W/mK.
 27. The roller according to claim 16, which comprises a hermetic sealing on one fibrous-web contact side of the roller.
 28. The roller according to claim 27, wherein said hermetic sealing is a filled epoxy resin having a thickness of between 2 and 10 mm.
 29. The roller according to claim 27, wherein said hermetic sealing is a thermal coating having a thickness of between 0.05 and 0.3 mm.
 30. The roller according to claim 16 configured for use in a press section or in a smoothing mill or a calender for smoothing or glazing a fibrous web.
 31. A method for manufacturing a roller, the method comprising the following steps: i) attaching a metal web containing a propellant on a roller core to form at least one layer on the roller core; ii) fixing the metal web on the roller core by a process selected from the group consisting of pressing, cold rolling, and winding and adhesive bonding; iii) supplying external heat for heating the layer containing the propellant so as to reach the melting range and thereby foam the material of the layer and to form a layer of foamed metallic material on the roller core; and to thereby produce the roller for use in a machine for manufacturing and/or processing and/or finishing a fibrous web, wherein the roller has the roller core and a roller covering formed of at least one layer or a plurality of layers, with the at least one layer or at least one of the layers being composed of the foamed metallic material.
 32. The method according to claim 31, which further comprises sealing the roller covering with a hermetic sealing by: i) grinding or re-turning the roller covering and, on account thereof, opening pores of the foamed metallic material close to a surface thereof; ii) attaching the hermetic sealing by pouring material that forms the hermetic sealing into the opened pores.
 33. A method for manufacturing a roller with a roller core and a covering, the method comprising the following steps: i) cold forming a planar, semi-finished product to form shell segments with a desired radius of the roller core; ii) foaming by way of a thermal process; iii) applying the shell segments to the roller core by way of an adhesive method, in order to produce at least one layer; iv) connecting the segments by way of a welding method or an adhesive method; to thereby form a roller for use in a machine for manufacturing and/or processing and/or finishing a fibrous web, such as a paper or cardboard web, with the roller having the roller core with a roller covering formed of at least one layer a plurality of layers of which at least one layer is composed of a foamed metallic material.
 34. The method according to claim 33, which further comprises sealing the roller covering with a hermetic sealing by: i) grinding or re-turning the roller covering and, on account thereof, opening pores of the foamed metallic material close to a surface thereof; ii) attaching the hermetic sealing by pouring material that forms the hermetic sealing into the opened pores. 